Linear measurement systems are used to determine linear movement of a movable device based on measured values obtained from some type of sensor. The values that are output from the sensor vary with linear movement of the movable device. The linear movement of the movable device is then calculated from the output values of the sensor. Linear measurement systems are commonly referred to as linear encoders.
Various types of linear encoders are used today including magnetic, optical, inductive, and capacitive linear encoders. Linear encoders are used in a variety of technologies including, for example, robotics systems, pick-and-place printed circuit board (PCB) systems, machine tools, semiconductor handling equipment, semiconductor test equipment, wire bonding systems, printers, laser scanners, coordinate-measuring machines, calipers, and tension testing equipment.
Optical linear encoders generally include a light source, a light sensor, a stationary scale, a controller, and other electrical circuitry. The light sensor is typically mechanically coupled to the movable device such that the sensor moves relative to the stationary scale as the movable device moves. The scale has reference marks or some other indicia on it that encodes position. The light source projects light onto the scale and the light sensor receives light reflected from the scale and generates electrical signals based on the received light. The electrical signals are converted into digital values by analog-to-digital conversion circuitry and then processed by the controller to decode the position of the movable device relative to the scale.
Although a variety of optical linear encoders are available in the market, existing optical linear encoders are relatively complex in design and expensive to manufacture. A need exists for an optical linear encoder that is relatively simple in design and relatively inexpensive to manufacture.